A generic antenna array usually comprises several radiators or radiator groups, but at least an arrangement of two stacked and two side-by-side radiators or radiator groups, so that a two-dimensional array layout results. For example, such a two-dimensional antenna array may exhibit four columns running vertically, arranged horizontally next to one another, each containing, for example, six to ten radiators or radiator groups arranged the vertical direction, offset one above the other. Depending on the purpose for which they are used, such antennas are sometimes also referred to as “smart antennas”, whose uses also include, for example, the tracking of targets (radar) in the military sphere. “Phased array” antennas are also frequently mentioned in these applications. Recently, however, these antennas are increasingly also being used in mobile telephony, particularly in the frequency ranges 800 MHz to 1000 MHz and 1700 MHz to 2200 MHz.
Through the development of new primary radiator systems, it has now also become possible to construct dual-polarized antenna arrays, in particular with a polarization alignment of +45° or −45° with respect to the horizontal or vertical.
Such antenna arrays, regardless of whether they are basically dual-polarized or merely consist of singly polarized radiators, can be used to determine the direction of the incoming signal. At the same time, however, by suitable adjustment of the phase angle of the transmission signals fed into the individual columns, it is also possible to alter the beam direction, i.e. a selective beam shaping is achieved.
This alignment of the beam direction of the antenna array in a different horizontal direction can be achieved by means of electronic beam tilting, i.e. the phase angles of the individual signals can be adjusted by suitable signal-processing means. Suitably dimensioned passive beam shaping networks are equally possible. The use of active or control-signal-driven phase shifters in these feeder networks for altering the beam direction is also known in the art. Such a beam shaping network may, for example, consist of what is known as a Butler matrix, which, for instance, has four inputs and four outputs. According to the input connected, the network generates a different, but fixed phase relationship between the radiators in the individual dipole arrays. Such an antenna construction using a Butler matrix is known in the art from U.S. Pat. No. 6,351,243 for example.
Electronic tilting of the horizontal field pattern can also be undertaken through the use of fixed-setting phases or by using phase shifters between the columns. The use of fixed-setting phases or phase shifters also allows the vertical radiated field pattern to be raised or lowered (down-tilting).
The antenna array can of course also be used such that the individual radiators or radiator groups in the individual columns are operated independently of one another, in order to be used independently of each other in a desired transmit or receive mode.
With regard to the individual radiators or radiator groups arranged in a column, such antenna arrays exhibit a radiated field pattern, whose lobe width running in the horizontal direction lies between roughly 80° and 100°.
Application areas are known, however, where a lobe width of the order of 60° to 65°, for example, is absolutely desirable.
Attempts have already been made to arrange the radiators or radiator groups in the individual columns in different horizontal positions. To a certain extent, this can affect the lobe width of the individual radiators or radiator groups of a column. Lobe widths of between 75° and 100° can be achieved by this means. A further reduction in the lobe width in this way, however, is generally not possible.
The exemplary illustrative non-limiting technology described herein creates an antenna array that, at least in one column and preferably in several or all columns, provides the means for lowering the horizontal lobe width of the radiators or radiator groups in the individual columns to values below 75°.
According to exemplary illustrative non-limiting implementations herein, it is possible, without the entire antenna structure becoming larger, to reduce the lobe width of the column radiators in that, in relation to the radiators or radiator groups arranged vertically one above the other in a column, at least an additional radiator or at least an additional radiator group is provided horizontally offset to this, which preferably is accommodated in an adjacent column. This at least one additional radiator, or this at least one additional radiator group, is not fed, however, with the radiators or radiator groups in the particular column in which they are arranged, but commonly with the radiators or radiator groups of the adjacent column. This allows the lobe width to be reduced significantly, whereby the optimum desired lobe width can be selected preferentially, in that the number of radiators or radiator groups assigned to a certain column but arranged offset to it is chosen in an appropriate way. In practice it has been shown, for example, that the use of two additional radiators or radiator groups in an antenna array that has six to twelve radiators or radiator groups arranged one above the other, is sufficient to achieve a lobe width of around 60° to 65°.
The solution according to exemplary illustrative non-limiting implementations herein can be applied if the radiators used in the individual columns consist of linearly polarized radiators, or dual polarized or circularly polarized radiators. All suitable radiators can be considered, for example dipole radiators in the form of conventional dipole radiators (particularly in the case of linearly polarized antennas) or, as another example, a dipole arrangement shaped in the manner of a dipole quad but radiating in the manner of a crossed dipole, as is basically known in the art from patents such as WO 00/39894. Equally, however, dipole quads or patch radiators etc. can also be used. With X-shaped radiator arrangements in particular, they can be aligned preferably in a +/−45° orientation in the horizontals or verticals.
The column spacing, i.e. the distance between the radiators or radiator groups between two adjacent columns is preferably about A/2 of the mean operating wavelength. However, this column spacing can, in principle, lie in a range from 0.25 A to 1.0 A of the operating wavelength, with the mean operating wavelength preferred. Preferred vertical spacing of the radiators in a column is 0.7 A to 1.2 A. Should an additional radiator or radiator group (which is fed commonly with the radiators in an adjacent column) be integrated in between, then the free clearance to a radiator or radiator group above or below reduces preferably to half the spacing.
As explained, the antenna according to exemplary illustrative non-limiting implementations can be operated such that the basic provision of radiators or radiator groups in a column can be fed and operated independently of those in an adjacent column (of course with the exception of the integrated additional radiators or radiator groups according to exemplary illustrative non-limiting implementations, which are fed commonly with those in an adjacent column). The originally provided radiators or radiator groups in a column are preferably drivable via phase shifters, via which a varying angle of declination with respect to a horizontal plane, or the down-tilt angle as it is known, can be selected.
As within the state of the art, with such an antenna array it is also possible to use integrated or retrofittable control devices, especially electromechanical ones, to perform a remotely controllable phase change with respect to the radiators or radiator groups assigned to the individual columns, such that a desired down-tilt setting can be made in each individual column.
With an antenna array of the kind described herein it is also possible to perform beam shaping of any desired type, particularly in the case where what is known as a Butler matrix or similar beam-shaping network is connected in series with the individual columns and the radiators or radiator groups provided there. As an alternative to this, hybrids can also be connected in the individual columns.
The columns are preferably uniformly spaced from one another, although antenna arrays with non-uniform spacing can be implemented.
The individual radiators or radiator groups in the individual columns can each be arranged at the same height or, alternatively, can each be vertically offset from one another. The middle position of a radiator or a radiator group in a column can be arranged at any relative vertical level to the respective position of the radiators or radiator groups provided there. The vertical offset can also correspond to exactly half the vertical spacing of two radiators or radiator groups arranged one above the other.
If the radiators or radiator groups are vertically offset from one another in two adjacent columns, this offers the advantage that the additionally provided radiators or radiator groups, which are assigned to a certain column but are placed in an adjacent column, can be arranged such that they come to lie at an equal height line next to a radiator or radiator group in the column they belong to. By this means, an optimized antenna can ultimately be implemented without its size increasing.
The additionally provided radiators or radiator groups for reducing the lobe width can be placed preferably centrally as well as at the upper and/or lower end of a column. They can also be placed in any position in between. Fine optimization can be carried out using these positioning measures.
In order to achieve the desired minimization of the lobe width, in exemplary illustrative non-limiting implementations herein, always at least one additional radiator or one additional radiator group is provided for a column, which for this purpose are integrated into an adjacent column horizontally or offset with horizontal or vertical components. The maximum number of these additional radiators or radiator groups equals N−1, where N corresponds to the number of originally provided radiators or radiator groups in a column.